Nasa rescue workers have described as "awesome" their operation to retrieve a capsule containing fragments of the asteroid Bennu
The container - which landed safely in the Utah desert at 08:52 local time (15:52 BST) - will now be inspected under sterile conditions in a so-called clean room
Its re-entry vehicle entered Earth's atmosphere at 27,000mph, withstood temperatures of 2,700C, then deployed parachutes to slow its descent
Scientists hope the material from the space rock can help explain how life on Earth began
They estimate the probe has 250g of dust onboard, but only time well tell how much has made it back from space
Bennu is regarded as the most dangerous rock in the Solar System because, although chances are slim, its path gives it the highest probability of hitting Earth of any known asteroid
We're less than 10 minutes away from Nasa's capsule landing in a desert in Utah.
Remember it's carrying asteroid samples, which could help explain how life on Earth began.
The space agency's running a countdown - we'll keep you updated with what it says.
In the last few minutes, Brian May - whose part in this mission we covered in our last post - has spoken of his immense pride to be part of the team.
"Happy sample return day!" he tells Nasa TV, as part of a special programme by the space agency to mark the moment the capsule lands on Planet Earth.
May adds that he can't be on the ground in Utah with everyone else because he is rehearsing for a Queen tour.
Jonathan Amos
Science correspondent
His is a face you may not have expected to see on this page. But Queen guitarist Sir Brian May - also an astrophysicist - played a critical role in helping to identify a place on Bennu where the Osiris-Rex spacecraft could grab its sample without destroying itself in the process.
May is an expert in stereoscopy - where he takes two pictures of a subject acquired from slightly different angles and aligns them to make a 3D view of a scene.
He and collaborator Claudia Manzoni did this for the shortlist of possible sample sites on Bennu. “I always say you need art as well as science," May told me, adding:
Quote MessageIt's like an artistic thing. You need to feel the terrain to know if the spaceship is likely to fall over or if it will hit this 'rock of doom' that was right on the edge of the eventual chosen site, called Nightingale. If that had happened it would have been disastrous. There were a billion dollars of American taxpayers’ money at stake."
Rebecca Morelle
Science editor, reporting from Utah
Image source, NasaThe dust and small rock fragments that scientists are eager to see will be split up and sent to researchers around the world.
The mission team will have access to the largest amount. About 4% of the sample will go to the Canadian Space Agency and 0.5% of it to the Japanese Space Agency in return for asteroid samples it sent to Nasa from the Hayabusa-2 mission.
Some of the material will also be stored at a secure facility in New Mexico.
Scientists around the world will also be able to ask for material.
The hope is that so much has been collected that there will be a bountiful resource for future generations of researchers.
Jonathan Amos
Science correspondent, reporting from Utah
While we wait for the capsule containing the sample of asteroid Bennu to land - expected in less than an hour - let's get back to understanding the significance of this mission.
This is not the first time material has been brought back to Earth from an asteroid. Japan has done it with the Hayabusa missions to the asteroids Itokawa and Ryugu.
While the Japanese managed to retrieve a little under 6g of material from their target rocks, there may be roughly 250g from Bennu inside the Osiris-Rex capsule.
This might not sound a lot, but it's actually a prodigious amount for the types of tests scientists want to do and will keep them busy for decades.
Aside from the Apollo missions which brought back kilos of Moon rock, Nasa has returned extra-terrestrial material to Earth on two other past ventures.
These include the 2006 Stardust mission which scooped up dust particles from around a comet. The Osiris-Rex capsule is based on the Stardust design.
As well as our text updates, you can watch the BBC News channel's coverage of the capsule landing in Utah right here on this page.
Just press the Play button at the the top of your screen.
Rebecca Morelle
Science editor, reporting from Utah
Four helicopters on the tarmac here at the military base have just taken off, heading off in a convoy silhouetted against the rising sun.
Onboard are the recovery team - poised to head to the capsule as soon as the landing location is revealed.
The capsule has no GPS tracker onboard so it will be spotted using long-range telescopes and infrared cameras.
It will be a great relief when the airborne team have the capsule in their sights as it descends towards the Utah desert.
We are hearing from our team on the ground, that the recovery teams have started to walk out to their helicopters.
"It’s getting serious now," BBC News' science correspondent Jonathan Amos tells us.
"The man of the moment, Osiris-Rex principal investigator Dante Lauretta, is onboard his chopper."
Dante Lauretta, principal investigator on the project, gets ready to board his helicopter
Jonathan Amos
Science correspondent, reporting from Utah
Scientists have been rehearsing their sample handling activities using simulated Bennu material.
Bennu is a carbonaceous asteroid. This means it has a lot of carbon in it, perhaps 5-10% by mass.
Scientists are expecting to see a mix of rocky fragments in a range of sizes - from a few millimetres across down to dust-sized.
The material will appear very dark, almost black, and very crumbly.
If the theory holds that life got started on the early Earth thanks to the delivery by impacting asteroids of important chemistry, then we might expect to see some fascinating organic molecules in the Bennu sample.
Molecules like amino acids are the building units of proteins.
Bennu will likely also have a lot of water bound up in its minerals, perhaps as much as 10% by mass.
And again, like the carbon chemistry, the delivery of water by impacting asteroids may help explain why we have so much H2O on our planet.
If you look at some carbonaceous meteorites, such as the famous Winchcombe meteorite that fell over the UK in 2021, they have water content that is a near exact chemical match to the water in our oceans.
It's safe to say the world's scientific community are excited about today's landing - and what the samples could show them about how life on Earth came to be.
Prof Sara Russell is a planetary scientist at the Natural History Museum in London - one of the institutions that's getting to analyse a piece of asteroid Bennu. She says:
Quote MessageWe've thought about it, we've talked about it, we've written papers about it, we've dreamt about what it's going to be and finally we are actually going to see it."
Mike Moreau is part of Nasa's team working on the project. He's more apprehensive and says his focus, for now, is on making sure the capsule arrives safely.
Quote MessageWe have some optical telescopes that can track and give us some confirmation that it released properly from the spacecraft, but otherwise we are just waiting until that atmospheric entry point."
Jonathan Amos
Science correspondent, reporting from Utah
Image source, Getty ImagesTardigrades, microscopic animals, are known to be able to survive some of the harshest conditions
In short, it's considered highly unlikely. Right now, the conditions on Bennu seem too tough and the resources too meagre.
It's certainly true there are some pretty crazy lifeforms on Earth that survive in the most hazardous environments, taming extremes of heat and cold, radiation and even the toxic presence of heavy metals.
Tardigrades, for example, are microscopic animals that have already demonstrated in experiments that they can withstand the vacuum of space for short periods.
But the chances of sustained life on a small asteroid - with its swings in temperature and constant bombardment from high-energy space particles - seem very remote indeed.
Rebecca Morelle
Science editor, reporting from Utah
There’s an important reason why scientists are trying to learn more about Bennu, the asteroid - it tops the list of Nasa’s most dangerous space rocks.
Every six years its orbit around the Sun brings it close to the Earth - sometimes dangerously so.
Scientists have calculated that the chance of it smashing into our planet stands at one in 1,750 in the next 300 or so years, and the date they are most worried about is 24 September 2182.
To put the odds in context, it’s the same as tossing a coin and getting heads 11 times in a row.
It’s a small risk but one scientists are taking seriously, because a strike from a 500m-wide space rock could cause utter devastation to a city the size of London and the surrounding areas.
So it makes sense to get up close and personal with Bennu. If we know what the asteroid is made of then we can come up with ways of stopping it - should we ever need to.
Image source, .Jonathan Amos
Science correspondent, reporting from Utah
Osiris-Rex: The moment a Nasa probe tagged an asteroid
The spacecraft had a 3m-long robotic arm that looked a little like a pogo stick, and held on the end of this stick was a large, disc-shaped collection mechanism.
I'm falling over metaphors here but imagine something resembling those old carousels for 35mm photo slideshows.
The idea was for Osiris-Rex to lower itself down to the asteroid, push the disc into the surface and at the same time give out a blast of nitrogen gas to kick up gravel and dust into the disc’s collection chamber.
But everyone got a bit of a shock.
When the disc touched the surface, it parted like a fluid, as if hitting a pool of water. By the time the gas fired, the disc was 10cm down.
The nitrogen pressure blasted a crater 8m in diameter. It was spectacular with material flying in all directions, but crucially also filling that collection chamber, which experts will soon get to analyse.
Jonathan Amos
Science correspondent, reporting from Utah
Nasa's Osiris-Rex mission was despatched from Earth in 2016 on a two-year, 2 billion km journey to Bennu, a mountain-sized asteroid that had been discovered at the turn of the century.
When the probe arrived in 2018 it set about making the most precise map of any object in the Solar System, detailing every lump and bump to a resolution of just 2cm.
Why? Because the goal was to grab a sample from Bennu's surface and bring it home to study in the laboratory.
Image source, NASA/University of ArizonaScientists needed to pick the best and safest place to snatch the prize, which Osiris-Rex completed in an audacious set of manoeuvres on 20 October 2020. Now that sample is nearly home.
Osiris-Rex has carried it back to Earth where, shortly, it will fall, inside a protective capsule, into the West Desert of the US state of Utah.
Jonathan Amos
Science correspondent, reporting from Utah
Good news. Twenty minutes after releasing the capsule, the Osiris-Rex spacecraft fired its engines to put itself on a new path.
This was a critical manoeuvre. If it hadn’t changed its trajectory, it would have followed the capsule into the atmosphere and destroyed itself.
The divert will instead see Osiris-Rex skim past the Earth at an altitude of about 800km (497 miles). This is around the height that many Earth observation imaging spacecraft orbit.
But Osiris-Rex won’t be hanging around - it’s got a new mission to rendezvous with another asteroid called Apophis. That’ll happen in 2029.
If the object moving through space is larger than about a metre across, it’s an asteroid.
If it’s less than a metre in diameter but bigger than a millimetre or so, it’s called a meteoroid.
Smaller still and it’s a micro-meteoroid.
When the object falls through the Earth’s atmosphere, it will heat up and produce a streak of light called a meteor. The terms shooting star or falling star are often used as well.
The more spectacular meteors are referred to as fireballs or bolides. A rock is not a meteorite until it lands on the Earth’s surface.
Image source, .Rebecca Morelle
Science editor, reporting from Utah
You may well be wondering why this mission is considered to be so important.
Asteroids are geological relics from the dawn of the Solar System. Some are even older than the planets - they formed from the swirling soup of gas and dust that marked the beginnings of our cosmic neighbourhood about 4.6 billion years ago.
Many have remained largely unchanged over billions of years, making them like perfectly preserved time capsules. Scientists think these space rocks played a vital role in our own history.
One idea is that asteroids impacted early Earth and delivered the essential ingredients - water and organic chemicals - that kick-started life here.
Soon scientists will get to find out if Bennu contains these biological building blocks, and whether asteroids played a role in making our world habitable.
Jonathan Amos
Science correspondent, reporting from Utah
About six hours before the planned re-entry time, the mission team voted to release the capsule from the Osiris-Rex spacecraft.
Just over two hours later, at 04:42 local time (11:42 BST) here at the Dugway military base, the command was executed.
The capsule with its precious cargo of samples of asteroid Bennu is now flying free through space bound for Planet Earth.
Jonathan Amos
Science correspondent, reporting from Utah
Image source, .The Osiris-Rex spacecraft is expected to hit the top of Earth's atmosphere at 08:42 local time (15:42 BST). The landing target is a remote military test range in western Utah.
The capsule will come in at the blistering pace of 12km/s, or 27,000mph.
As it pushes up against the air, its underside will get extremely hot - more than 3,000C - but, crucially, this fiery plunge will also slow the capsule down.
A drogue parachute will open for stability, followed then by a main chute to bring the capsule gently to the ground.
Contact with the Utah desert floor is expected at 08:55. Helicopters will then bring it to a temporary laboratory where it can be prepared for onward travel to Nasa's Johnson Space Center in Texas.
It's there that a dedicated facility has been built to analyse the Bennu samples.
Image source, .Rebecca Morelle
Science editor, reporting from Utah
The Sun’s not yet up here at the Dugway military base in Utah, but the mission team is busy with the final preparations for this dramatic conclusion to their seven year mission.
Four helicopters are lined up on the tarmac, ready to take the recovery specialists out to the landing zone as soon as the capsule comes down.
The feeling here is one of anxious excitement - they’ve practised and practised for this moment and there’s no going back now.
The mission lead told us that he’s 99% sure everything will go to plan - but it’s the other 1% that’s been keeping him awake at night.